Could this introduce test flakiness due to a race condition?
I don't think so. test_tcp_forwarding_ip() waits for both socat
processes and compares both output files before check_priority() reads
the counters, so the connection is closed by then.
check_dscp() reads and resets its counters the same way, and its
"dscp_ingress" check also expects zero after the "dscp_none" run
counted packets:
check_dscp "dscp_none" "0"
...
check_dscp "dscp_ingress" "$pmtu"
The test passed three times out of three with the series. No change
planned for this one.